1. Field of the Invention
The present invention relates to a hydrogenated copolymer. More particularly, the present invention is concerned with a hydrogenated copolymer obtained by hydrogenating an unhydrogenated copolymer comprising conjugated diene monomer units and vinyl aromatic monomer units, the unhydrogenated copolymer having at least one polymer block (H) of vinyl aromatic monomer units, wherein the content of the vinyl aromatic monomer units, content of the polymer block (H), weight average molecular weight, and hydrogenation ratio (as measured with respect to the double bonds in the conjugated diene monomer units) of the hydrogenated copolymer are, respectively, within specific ranges, and substantially no crystallization peak is observed at −50 to 100° C. in a differential scanning calorimetry (DSC) chart obtained with respect to the hydrogenated copolymer. The hydrogenated copolymer of the present invention not only has excellent flexibility, impact resilience and scratch resistance, but also has excellent handling property (anti-blocking property). The “anti-blocking property” means a resistance to adhesion phenomena (which is generally referred to as “blocking”) wherein when, for example, stacked resin shaped articles or a rolled resin film (which have or has resin surfaces which are in contact with each other) are or is stored for a long time, unfavorably strong adhesion occurs between the resin surfaces, so that it becomes difficult to separate the resin surfaces from each other. Further, the present invention also relates to a hydrogenated copolymer composition comprising the above-mentioned hydrogenated copolymer (a), and at least one polymer (b) selected from the group consisting of a thermoplastic resin other than the hydrogenated copolymer (a) and a rubbery polymer other than the hydrogenated copolymer (a). The hydrogenated copolymer composition comprising the excellent hydrogenated copolymer of the present invention exhibits excellent properties, such as high impact resistance, moldability and abrasion resistance. Each of the hydrogenated copolymer and hydrogenated copolymer composition of the present invention can be advantageously used as a foam, various shaped articles, a building material, a vibration damping, soundproofing material, an electric wire coating material and the like.
2. Prior Art
A copolymer comprising a conjugated diene and a vinyl aromatic hydrocarbon (hereinafter, frequently referred to as a “conjugated diene/vinyl aromatic hydrocarbon copolymer”) has unsaturated double bonds, so that such a copolymer have poor thermal stability, weatherability and ozone resistance. As a method for improving these properties of the conjugated diene/vinyl aromatic hydrocarbon copolymer, there has long been known a method in which the unsaturated double bonds of the copolymer are hydrogenated. Such a method is disclosed in, for example, Unexamined Japanese Patent Application Laid-Open Specification No. Sho 56-30447 and Unexamined Japanese Patent Application Laid-Open Specification No. Hei 2-36244.
On the other hand, a hydrogenation product of a conjugated diene/vinyl aromatic hydrocarbon block copolymer exhibits, even if not vulcanized, not only excellent elasticity at room temperature, which is comparable to that of a conventional vulcanized natural or synthetic rubber, but also excellent processibility at high temperatures, which is comparable to that of a conventional thermoplactic resin. Therefore, the hydrogenated block copolymer is widely used in various fields, such as modifiers for plastics, adhesive agents, automobile parts, and parts for medical equipment. In recent years, it has been attempted to obtain a random copolymer of a conjugated diene and a vinyl aromatic hydrocarbon, which has characteristics similar to those of the hydrogenated block copolymer as mentioned above.
For example, Unexamined Japanese Patent Application Laid-Open Specification No. Hei 2-158643 (corresponding to U.S. Pat. No. 5,109,069) discloses a composition containing a hydrogenated diene copolymer and a polypropylene resin, wherein the hydrogenated diene copolymer is obtained by hydrogenating a random copolymer of a conjugated diene and a vinyl aromatic hydrocarbon, which random copolymer has a vinyl aromatic hydrocarbon content of 3 to 50% by weight, a molecular weight distribution (weight average molecular weight (Mw)/number average molecular weight (Mn)) of 10 or less, and a vinyl bond content of 10 to 90% as measured with respect to the conjugated diene monomer units in the copolymer. Further, Unexamined Japanese Panent Application Laid-Open Specification No. Hei 6-287365 discloses a composition containing a hydrogenated diene copolymer and a polypropylene resin, wherein the hydrogenated diene polymer is obtained by hydrogenating a random copolymer of a conjugated diene and a vinyl aromatic hydrocarbon, which random copolymer has a vinyl aromatic hydrocarbon content of 5 to 60% by weight, and a vinyl bond content of 60% or more as measured with respect to the conjugated diene monomer units in the copolymer.
With respect to the above-mentioned hydrogenated diene copolymers, it has been attempted to use the copolymers as substitutes for a flexible vinyl chloride resin. The flexible vinyl chloride resin causes environmental problems, such as generation of halogen gas when the resin is on fire, and generation of enrivonmental hormones due to the plasticizer used in the resin. Therefore, there is a pressing need for development of a substitute material for the flexible vinyl chloride resin. However, the above-mentioned hydrogenated diene copolymers are unsatisfactory with resepct to the properies (such as impact resilience, and scratch resistance) which are needed for a material used as a substitute for the flexible vinyl chloride resin.
Further, with respect to molding materials containing the above-mentioned hydrogenated diene copolymer in combination with vairous theremoplastic resins or rubbers, it has been desired to improve the mechanical strength and moldability of the hydrogenated diene copolymer.
WO98/12240 discloses a molding material composed mainly of, as a polymer similar to the vinyl chloride resin, a hydrogenated block copolymer comprising a polymer block composed mainly of styrene and a polymer block composed mainly of butadiene and styrene. Further, Unexamined Japanese Patent Application Laid-Open Specification No. Hei 3-185058 discloses a resin composition comprising a polyphenylene ether resin, a polyolefin resin, and a hydrogenation product of a vinyl aromatic hydrocarbon/conjugated diene copolymer, wherein the same hydrogenated block copolymer as used in the above-mentioned WO98/12240 is used as the hydrogenation product of a vinyl aromatic hydrocarbon/conjugated diene copolymer. However, the hydrogenated copolymer used in each of the above-mentioned patent documents is a crystalline polymer and, hence, has poor flexibility and is not suitable for use as a substitute for the flexible vinyl chloride resin.
Thus, although there has been a pressing need for development of a substitute material for the flexible vinyl chloride resin, a material having excellent properties (such as flexibility and scratch resistance) which are comparable to those of the flexible vinyl chloride resin has not yet been obtained.